1. Field of the Invention
It is not presently known how to manufacture large-volume balloons capable of withstanding high overpressures while being lightweight enough for practical use. Thus the presently known airships used for shipping high loads have envelope structures capable of withstanding overpressures only up to about 10 millibars (difference between internal and external pressures) before deterioration begins. Under these conditions the variations in the gas masses which can be induced in these balloons are far too inadequate to assure their aerostatic steering in the vertical direction. This steering must necessarily be produced by varying solid or liquid masses, which entails several well known drawbacks (poor steering control during descent, necessity to take on additional loads, precautions required by jettison actions . . . ). Also the aerostatic equilibrium of such balloons is very sensitive to thermal variations and to fuel consumption, and steering the balloon is a delicate operation.
There are also steerable space balloons to carry a payload for the exploration of the atmospheric layers. Again when these balloons are of high volume, their overpressure is low, and as a rule they comprise a carrier balloon inflated with a lighter-than-air gas such as helium and a stabilizer balloon inflated with air and joined to the former and located underneath it. The steering is carried out by varying the pressure of the constant-volume stabilizer balloon by subjecting it to an intake or an exhaust of air. These systems suffer from drawbacks related to the fact that the steering forces are produced solely by the stabilizer balloon: changes in levels are slow to come about and altitude is difficult to control, and at their top altitudes, these balloons also are unstable.
2. Objects of the Invention
The present invention proposes to overcome the drawbacks stated above of the known steered aerostatic balloons.
One essential object of the invention is to provide an aerostatic balloon of which the volume can be very large (up to 10.sup.6 m.sup.3) so as to be capable of transporting high loads, and of which the gas-retaining structure can withstand very high overpressures (several hundred millibars).
Accordingly it is an object of the invention to provide a balloon which can be aerostatically steered by varying the gas masses.
Another object of the invention is to increase substantially the effectiveness of the steering actions (in the vertical direction) in order to make possible rapid and well controlled changes in level regardless of altitude.
Another object is to achieve good balloon stability regardless of altitude and in particular at the upper limit.
Still another object is to make easier the ground-based balloon launching operations.